Methods for triggering a base station to transmit a MAC message

ABSTRACT

The examples described herein provide for a Secondary Base Station (SeNB) Change procedure in a system configured to provide Dual Connectivity, where the SeNB Change procedure does not include the RACH procedure. As part of the SeNB Change procedure, a UE device generates a request that the Target Secondary base station (Target SeNB) is to send a Media Access Control (MAC) message to the UE device. In some examples, the request can be configured to specify a particular MAC Control Element that the Target SeNB should send in response to receiving the request. Upon receipt of the request, the Target SeNB transmits the requested MAC message to the UE device, along with TA information, if required. The UE device determines when the SeNB Change procedure has been completed, based at least partially on when the requested MAC message is received from the Target SeNB.

CLAIM OF PRIORITY

The present application is a continuation of U.S. application Ser. No.16/347,103, filed May 2, 2019 and entitled “METHODS FOR TRIGGERING ABASE STATION TO TRANSMIT A MAC MESSAGE”; which is a national stageapplication of PCT/US2017/059838, filed Nov. 3, 2017 and entitled“METHODS FOR TRIGGERING A BASE STATION TO TRANSMIT A MAC MESSAGE”; whichclaims priority to Provisional Application No. 62/417,507, entitled“METHODS FOR TRIGGERING AN ENB TO TRANSMIT A MAC MESSAGE”; filed Nov. 4,2016, all of which are assigned to the assignee hereof, and herebyexpressly incorporated by reference.

FIELD

This invention generally relates to wireless communications and moreparticularly to user equipment devices requesting messages from basestations.

BACKGROUND

In conventional systems, a handover of a user equipment (UE) device froma source base station (e.g., source eNB) to a target base station (e.g.,target eNB) involves the source base station transmitting a HandoverRequest message to the target base station (e.g., to initiate ahandover) and the target base station transmitting a message inresponse. The source base station signals target base station uplinkresources to the UE device, which utilizes the uplink resources for aRandom-Access Channel (RACH) procedure. After the UE device is handedover to the target base station, the UE device transmits an uplinksignal to the target base station as part of the RACH procedure. Thetarget base station uses the uplink signal received from the UE deviceto calculate a Timing Advance (TA), which is needed in order for the UEdevice's uplink transmissions to be synchronized to the target basestation after handover. The target base station signals the TA in theRandom Access Response (RAR) message, along with uplink resources neededfor the UE device to obtain uplink access to the target base station aspart of the handover procedure. The UE device determines when thehandover procedure is completed for the UE device, based upon when theUE device receives the RAR message. In conventional systems configuredto provide Dual Connectivity, a Secondary Base Station (SeNB) Change ofa UE device from a source SeNB to a target SeNB makes use of a similarRACH procedure.

SUMMARY

The examples described herein provide for a Secondary Base Station(SeNB) Change procedure in a system configured to provide DualConnectivity, where the SeNB Change procedure does not include the RACHprocedure. As part of the SeNB Change procedure, a UE device generates arequest that the Target Secondary base station (Target SeNB) is to senda Media Access Control (MAC) message to the UE device. In some examples,the request can be configured to specify a particular MAC ControlElement that the Target SeNB should send in response to receiving therequest. Upon receipt of the request, the Target SeNB transmits therequested MAC message to the UE device, along with TA information, ifrequired. The UE device determines when the SeNB Change procedure hasbeen completed based at least partially on when the requested MACmessage is received from the Target SeNB.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a communication system for an example inwhich a UE device requests that a target secondary base stationtransmits a MAC message to the UE device.

FIG. 2A is a block diagram of an example of the base stations shown inFIG.

FIG. 2B is a block diagram of an example of the UE device shown in FIG.1 .

FIG. 3A is a messaging diagram of an example of the messages exchangedbetween the various system components shown in FIG. 1 .

FIG. 3B is a block diagram of an example of a MAC Protocol Data Unitstructure.

FIG. 4 is a flowchart of an example of a method in which a UE devicerequests that a target secondary base station transmits a MAC message tothe UE device.

DETAILED DESCRIPTION

The Timing Advance (TA) provided by a target base station to a UE deviceduring a handover in conventional systems is needed in order for the UEdevice's uplink transmissions to be synchronized to the target basestation after handover. If the uplink transmissions are not properlysynchronized to the target base station, the target base station willnot be able to detect and decode the transmissions. However, onedrawback of conventional systems is that the TA determination stepincreases the amount of time required to complete the handover procedurein examples when the TA may not need to be determined during a handover.

RACH-less handovers can be used in examples when the TA does not need tobe determined during a handover, in order to reduce the time required tocomplete the handover procedure. As used herein, the term “RACH-lesshandover” refers to skipping the transmission of the Random-AccessChannel (RACH) by the user equipment (UE) device to the target basestation (e.g., target eNB) during handover, which significantly improvesthe delay for the handover procedure since the RACH procedure is asubstantial part of the handover delay. However, if the RACH procedureis not performed, any alternative method must provide a way for the UEdevice to be able to determine when a handover of the UE device has beensuccessfully completed, which is determined by receiving the RAR messagein conventional systems.

Besides the foregoing requirements, a RACH-less handover procedureperformed in a 3rd Generation Partnership Project Long Term Evolution(3GPP LTE) system that is configured to provide Dual Connectivity to UEdevices requires similar considerations. For example, Dual Connectivity(DC) allows UE devices to exchange data simultaneously from differentbase stations, also referred to as eNodeBs (eNBs), in order to boost theperformance in a heterogeneous network with dedicated carrierdeployment. Dual Connectivity in an LTE network can significantlyimprove per-user throughput and mobility robustness by allowing users tobe connected simultaneously to a master cell group (MCG) and a secondarycell group (SCG) via a Master eNB (MeNB) and Secondary eNB (SeNB),respectively. In such a system, as a UE device moves or radio conditionschange, the UE device may maintain a primary connection with the sameMeNB but may have a secondary connection that is handed over from afirst SeNB (e.g., Source SeNB) to a second SeNB (e.g., Target SeNB).This type of handover in a system that provides Dual Connectivity isknown as a Secondary base station (SeNB) Change procedure.

The examples described herein illustrate various techniques forperforming RACH-less SeNB Change procedures. For example, the MeNBtransmits an uplink grant to the UE device in a Radio Resource Control(RRC) Connection Reconfiguration message. The uplink grant provides theresources for the UE device to transmit an uplink transmission to aTarget SeNB. Upon receipt of the RRC Connection Reconfiguration messagefrom the Master eNB, the UE device generates a request that the TargetSeNB is to send a MAC message to the UE device. The UE device transmitsthe request using the uplink grant received in the RRC ConnectionReconfiguration message.

Upon receipt of the request, the Target SeNB transmits the requested MACmessage to the UE device, along with TA information, if required. The UEdevice determines when the SeNB Change procedure has been completed,based at least partially on when the requested MAC message is receivedfrom the Target SeNB. Any unnecessary information received in the MACmessage may be discarded by the UE device.

FIG. 1 is a block diagram of a communication system for an example inwhich a UE device requests that a target secondary base station (TargetSeNB) transmits a MAC message to the UE device. The communication system100 is part of a radio access network (not shown) that provides variouswireless services to UE devices that are located within the respectiveservice areas of the various base stations that are part of the radioaccess network.

In the interest of clarity and brevity, communication system 100 isshown as having only one Master base station (MeNB) 102 and only twoSecondary base stations (SeNBs) 104, 105. However, in other examples,communication system 100 could have any suitable number of Master basestations and Secondary base stations. In the example of FIG. 1 , atleast a portion of the service area (cell) for Master base station 102is represented by cell 108. At least a portion of the respective serviceareas (cells) for Secondary base stations 104, 105 are represented bycells 112, 116. Cells 108, 112, 116 are represented by ovals, but atypical communication system 100 would have a plurality of cells, eachhaving variously shaped geographical service areas. Moreover, althoughcell 108 is shown as only partially overlapping cells 112, 116 in theexample of FIG. 1 , one, or both, of cells 112, 116 may be locatedentirely within cell 108, in other examples.

Base stations 102, 104, 105, sometimes referred to as eNodeBs or eNBs,communicate with the wireless user equipment (UE) device 106 byrespectively transmitting downlink signals 110, 114, 122 when connectedto UE device 106. Base stations 102, 104, 105 respectively receiveuplink signals 118, 120, 124 transmitted from the UE device 106 whenconnected to UE device 106. The UE device 106 is any wirelesscommunication device such as a mobile phone, a transceiver modem, apersonal digital assistant (PDA), a tablet, or a smartphone, forexample.

Base stations 102, 104, 105 are connected to the network through abackhaul (not shown) in accordance with known techniques. As shown inFIG. 2A, Master base station 102 comprises controller 204, transmitter206, and receiver 208, as well as other electronics, hardware, and code.Although FIG. 2A specifically depicts the circuitry and configuration ofMaster base station 102, the same base station circuitry andconfiguration that is shown and described in connection with Master basestation 102 is also utilized for Secondary base stations 104, 105, inthe example shown in FIG. 1 . In other examples, one, or both, of theSecondary base stations 104, 105 may have circuitry and/or aconfiguration that differs from that of the Master base station 102.

The Master base station 102 is any fixed, mobile, or portable equipmentthat performs the functions described herein. The various functions andoperations of the blocks described with reference to the Master basestation 102 may be implemented in any number of devices, circuits, orelements. Two or more of the functional blocks may be integrated in asingle device, and the functions described as performed in any singledevice may be implemented over several devices.

For the example shown in FIG. 2A, the Master base station 102 may be afixed device or apparatus that is installed at a particular location atthe time of system deployment. Examples of such equipment include fixedbase stations or fixed transceiver stations. In some situations, theMaster base station 102 may be mobile equipment that is temporarilyinstalled at a particular location. Some examples of such equipmentinclude mobile transceiver stations that may include power generatingequipment such as electric generators, solar panels, and/or batteries.Larger and heavier versions of such equipment may be transported bytrailer. In still other situations, the Master base station 102 may be aportable device that is not fixed to any particular location.Accordingly, the Master base station 102 may be a portable user devicesuch as a UE device in some circumstances.

The controller 204 includes any combination of hardware, software,and/or firmware for executing the functions described herein as well asfacilitating the overall functionality of the Master base station 102.An example of a suitable controller 204 includes code running on amicroprocessor or processor arrangement connected to memory. Thetransmitter 206 includes electronics configured to transmit wirelesssignals. In some situations, the transmitter 206 may include multipletransmitters. The receiver 208 includes electronics configured toreceive wireless signals. In some situations, the receiver 208 mayinclude multiple receivers. The receiver 208 and transmitter 206 receiveand transmit signals, respectively, through an antenna 210. The antenna210 may include separate transmit and receive antennas. In somecircumstances, the antenna 210 may include multiple transmit and receiveantennas.

The transmitter 206 and receiver 208 in the example of FIG. 2A performradio frequency (RF) processing including modulation and demodulation.The receiver 208, therefore, may include components such as low noiseamplifiers (LNAs) and filters. The transmitter 206 may include filtersand amplifiers. Other components may include isolators, matchingcircuits, and other RF components. These components in combination orcooperation with other components perform the base station functions.The required components may depend on the particular functionalityrequired by the base station.

The transmitter 206 includes a modulator (not shown), and the receiver208 includes a demodulator (not shown). The modulator modulates thesignals to be transmitted as part of the downlink signals 110 and canapply any one of a plurality of modulation orders. The demodulatordemodulates any uplink signals 118 received at the Master base station102 in accordance with one of a plurality of modulation orders.

Returning to FIG. 1 , the communication system 100 provides variouswireless services to UE device 106 via base stations 102, 104, 105. Forthe examples herein, the communication system 100 operates in accordancewith at least one revision of the 3rd Generation Partnership ProjectLong Term Evolution (3GPP LTE) communication specification. UE device106 is initially served by Master base station 102 and by Source SeNB(S-SeNB) 104. Thus, UE device 106 receives downlink signals 110, 114 viaantenna 212 and receiver 214, as shown in FIG. 2B. Besides antenna 212and receiver 214, UE device 106 further comprises controller 216 andtransmitter 218, as well as other electronics, hardware, and code. UEdevice 106 is any fixed, mobile, or portable equipment that performs thefunctions described herein. The various functions and operations of theblocks described with reference to UE device 106 may be implemented inany number of devices, circuits, or elements. Two or more of thefunctional blocks may be integrated in a single device, and thefunctions described as performed in any single device may be implementedover several devices.

The controller 216 includes any combination of hardware, software,and/or firmware for executing the functions described herein as well asfacilitating the overall functionality of a UE device. An example of asuitable controller 216 includes code running on a microprocessor orprocessor arrangement connected to memory. The transmitter 218 includeselectronics configured to transmit wireless signals. In some situations,the transmitter 218 may include multiple transmitters. The receiver 214includes electronics configured to receive wireless signals. In somesituations, the receiver 214 may include multiple receivers. Thereceiver 214 and transmitter 218 receive and transmit signals,respectively, through antenna 212. The antenna 212 may include separatetransmit and receive antennas. In some circumstances, the antenna 212may include multiple transmit and receive antennas.

The transmitter 218 and receiver 214 in the example of FIG. 2B performradio frequency (RF) processing including modulation and demodulation.The receiver 214, therefore, may include components such as low noiseamplifiers (LNAs) and filters. The transmitter 218 may include filtersand amplifiers. Other components may include isolators, matchingcircuits, and other RF components. These components in combination orcooperation with other components perform the UE device functions. Therequired components may depend on the particular functionality requiredby the UE device.

The transmitter 218 includes a modulator (not shown), and the receiver214 includes a demodulator (not shown). The modulator can apply any oneof a plurality of modulation orders to modulate the signals to betransmitted as part of the uplink signals 118, 120, 124 which are shownin FIG. 1 . The demodulator demodulates the downlink signals 110, 114,122 in accordance with one of a plurality of modulation orders.

At the beginning of operation of the example shown in FIG. 1 , the UEdevice 106 is being served by Master base station 102 and Source SeNB104. Thus, upon receipt of the downlink signals 110, 114, the UE device106 demodulates the downlink signals 110, 114, which yields encoded datapackets that contain data pertaining to at least one of the wirelessservices that the Master base station 102 and the Source SeNB 104 areproviding to the UE device 106. The UE device 106 decodes the encodeddata packets, using controller 216, to obtain the data.

When the Secondary base station (SeNB) Change procedure criteria aremet, the SeNB Change procedure is initiated. The SeNB Change procedurecriteria may include, for example, radio congestion at Source SeNB 104,poor/deteriorating signal quality for the uplink/downlink signals for UEdevice 106, and/or underutilization of available resources by TargetSeNB 105. However, any other suitable criteria could be used. Asmentioned above, when performing the SeNB Change procedure, the UEdevice 106 maintains its primary connection with the Master base station102 but hands over its secondary connection from the Source SeNB 104 tothe Target SeNB 105.

To initiate the SeNB Change procedure, the Master base station 102transmits an SeNB Addition Request to Target SeNB 105 via a wired (e.g.,X2) or a wireless communication link. If the transmission is wireless,Master base station 102 uses transmitter 206 and antenna 210 to transmitthe SeNB Addition Request, and Target SeNB 105 receives the wirelesstransmission of the SeNB Addition Request via its antenna 210 andreceiver 208. The transmission of the SeNB Addition Request to theTarget SeNB 105 is represented in FIG. 3A by signal 302.

If the Target SeNB 105 agrees to serve as the SeNB for UE device 106,the Target SeNB 105 sends an SeNB Addition Request Acknowledgementmessage to the Master base station 102 via a wired connection or awireless connection. The transmission of the SeNB Addition RequestAcknowledgement is represented in FIG. 3A by signal 304. Upon receipt ofthe SeNB Addition Request Acknowledgement, the Master base station 102transmits an SeNB Release Request to Source SeNB 104 via a wired (e.g.,X2) or a wireless communication link, which informs the Source SeNB 104that the secondary connection of the UE device 106 is being handed overto Target SeNB 105. The transmission of the SeNB Release Request messageis represented in FIG. 3A by signal 306.

The Master base station 102 transmits a Radio Resource Control (RRC)Connection Reconfiguration message to the UE device 106. The RRCConnection Reconfiguration message includes uplink grant information,which the UE device 106 will utilize to send a request that the TargetSeNB 105 transmits a Media Access Control (MAC) message to the UE device106. The RRC Connection Reconfiguration message may also includeinformation that is used by the UE device 106 to detect and decode theMAC message that the Target SeNB 105 will send to the UE device 106. TheRRC Connection Reconfiguration message may also include informationregarding the length of a window during which the UE device 106 shouldmonitor the Physical Downlink Control Channel (PDCCH) for a RAR messagethat will be sent by the Target SeNB 105. The transmission of the RRCConnection Reconfiguration message is represented in FIG. 3A by signal308.

Once the RRC Connection is reconfigured, the UE device 106 transmits anRRC Connection Reconfiguration Complete message to the Master basestation 102. The RRC Connection Reconfiguration Complete message isrepresented in FIG. 3A by signal 310. Upon receipt of the RRC ConnectionReconfiguration Complete message, the Master base station 102 transmitsan SeNB Reconfiguration Complete message to Target SeNB 105 to informTarget SeNB 105 that (1) UE device 106 has been reconfigured to switchits secondary connection from Source SeNB 104 to Target SeNB 105, and(2) Target SeNB 105 should be prepared to receive an uplink transmissionfrom UE device 106. The SeNB Reconfiguration Complete message isrepresented in FIG. 3A by signal 312.

Upon receipt of the RRC Connection Reconfiguration message, the UEdevice 106 generates a request that the Target SeNB 105 transmits a MACmessage to the UE device 106. In some examples, the request comprises aLogical Channel Identifier (LCID) located in a subheader of a MACProtocol Data Unit (PDU) that will be transmitted to the Target SeNB105. FIG. 3B shows an example of a MAC PDU structure 320, whichcomprises a MAC header 322 and a MAC payload 324. The MAC header 322comprises one or more subheaders 326 that identify the type ofinformation contained in the MAC payload 324. There is a subheader 326associated with each entry in the MAC payload 324. As can be seen inFIG. 3B, the first part of the MAC payload 324 contains one or more MACControl Elements 328 that are followed by one or more MAC Service DataUnits (SDUs) 330. The MAC SDUs include control data, such as an RRCmessage, and user data. For the example shown in FIG. 3B, subheader 1 isassociated with MAC Control Element 328, and subheader 2 is associatedwith MAC SDU 330.

In some examples, the LCID, itself, is defined to request that theTarget SeNB 105 transmits a specific MAC Control Element, such as a UEContention Resolution Identity MAC Control Element, to the UE device106. For these examples, only the LCID located in a subheader (e.g.,subheader 1) is used to request a specific MAC Control Element or otherMAC message, and no payload information is needed for the request. Inother examples, the request is that the Target SeNB 105 is to transmit aRandom Access Response (RAR) message to the UE device 106.

Alternatively, the LCID can be a generic MAC Command Request, indicatingthat a MAC Control Element located in the MAC payload 324 identifies therequested command. For example, the LCID, which is included in asubheader 326 of the MAC PDU 320, is set to the MAC Command Requestvalue, and the specific MAC Control Element or MAC message beingrequested (e.g., UE Contention Resolution Identity or RAR) is identifiedby a value located in a MAC SDU 330 that corresponds with the subheaderthat contains the MAC Command Request LCID.

In some examples, any MAC message transmitted to the Target SeNB 105using the uplink grant information received in the RRC ConnectionReconfiguration message of the SeNB Change procedure is a request thatthe Target SeNB 105 transmits a MAC message to the UE device 106. Insome examples, receiving the SeNB Reconfiguration Complete message is arequest that the Target SeNB 105 transmits a MAC message to the UEdevice 106.

For the examples described herein, MAC messages contain controlinformation that originates and terminates in peer MAC layer (Layer 2)protocol entities, such as specified in the 3rd Generation PartnershipProject Long Term Evolution (3GPP LTE) MAC specification, for example,and includes MAC messages, such as the Random Access Response (RAR)message, as well as MAC Control Elements.

Regardless of the format of the request that the Target SeNB 105 is totransmit a MAC message, the UE device 106 transmits, via transmitter 218and antenna 212, the request to the Target SeNB 105 in an uplinktransmission 124. In these examples, the transmission of the request tothe Target SeNB 105 is represented in FIG. 3A by signal 314.

The Target SeNB 105 receives the request via antenna 210 and receiver208. Upon receipt of the request, the Target SeNB 105 utilizescontroller 204 to generate a MAC message in accordance with the receivedrequest. More specifically, in some examples, the Target SeNB 105generates a MAC message that contains the specific MAC Control Elementindicated in the request from the UE device 106. For example, if therequest was for a UE Contention Resolution Identity MAC Control Element,then the Target SeNB 105 would generate a MAC message containing a UEContention Resolution Identity MAC Control Element. Likewise, if therequest was for a RAR, then the Target SeNB 105 would generate a MACmessage containing a RAR.

The Target SeNB 105 transmits, via transmitter 206 and antenna 210, theMAC message containing the requested MAC message (e.g., a UE ContentionResolution Identity MAC Control Element or a RAR) to the UE device 106.The transmission of the MAC message is represented in FIG. 3A by signal316.

After transmission of the request, the UE device 106 monitors thePhysical Downlink Control Channel (PDCCH) to receive the MACtransmission that is sent by the Target SeNB 105 in response to therequest. In an embodiment where the request was for a Random Access (RA)Response, the UE device 106 monitors the PDCCH during a PDCCH RandomAccess (RA) Response window that has a size that is obtained from SystemInformation or from Mobility Control Information contained in the RRCConnection Reconfiguration message. In some examples, the PDCCH RAResponse window starts at a subframe in which the request wastransmitted to the Target SeNB 105 or at a point relative to a subframein which the request was transmitted to the Target SeNB 105. Forexample, the PDCCH RA Response window can be configured to start at thesubframe that contains the end of the request (e.g., MAC message)transmitted by the UE device 106 or at the subframe that contains theend of the request (e.g., MAC message) transmitted by the UE device 106plus three subframes. In other examples, the PDCCH RA Response windowstarts at a subframe value included in Random Access Channel (RACH)parameters provided by the Target SeNB 105 or at the subframe valueincluded in the RACH parameters provided by the Target SeNB 105 plusthree subframes. The three additional subframes referenced in theforegoing examples are based on current LTE specifications. However, anyother suitable subframe offsets (e.g., a different number of additionalsubframes) may be used.

For the UE device 106 to receive the RAR message via antenna 212 andreceiver 214 during the PDCCH RA Response window, the UE device 106utilizes controller 216 to determine a Random Access Radio NetworkTemporary Identifier (RA-RNTI) using a subframe index associated with asubframe in which the request was transmitted by the UE device 106. Inother examples, the UE device 106 utilizes controller 216 to determinethe RA-RNTI using a subframe index associated with a subframe valueincluded in Random Access Channel (RACH) parameters provided by theTarget SeNB 105. Regardless of the method used to determine the RA-RNTI,the RA-RNTI indicates which UE device is the target of the RAR messagetransmitted by the Target SeNB 105. Thus, the UE device 106 utilizes theRA-RNTI to confirm that the received RAR message is, in fact, intendedfor the UE device 106.

In an embodiment where the request was for a MAC message or a MACControl Element, the UE device 106 monitors the PDCCH to receive adownlink assignment on the Physical Downlink Shared Channel (PDSCH) thatcontains the MAC message.

Based at least partially upon when the UE device 106 receives therequested MAC message, the UE device 106 uses controller 216 todetermine when the SeNB Change procedure (e.g., from Source SeNB 104 toTarget SeNB 105) is completed for the UE device 106.

FIG. 3A is a messaging diagram of an example of the messages exchangedbetween the various system components shown in FIG. 1 . In this example,the Master base station 102 transmits an SeNB Addition Request to TargetSeNB 105, via signal 302. In response, Target SeNB 105 transmits an SeNBAddition Request Acknowledgement to the Master base station 102 viasignal 304. Upon receipt of the SeNB Addition Request Acknowledgement,the Master base station 102 transmits an SeNB Release Request to theSource SeNB 104 via signal 306.

The Master base station 102 transmits an RRC Connection Reconfigurationmessage to the UE device 106, which is represented by signal 308. Asmentioned above, the RRC Connection Reconfiguration message may contain(1) uplink grant information required by the UE device 106, (2)information that is used by the UE device 106 to detect and decode theMAC message that the Target SeNB 105 will send to the UE device 106, and(3) information regarding the length of a window during which the UEdevice 106 should monitor the Physical Downlink Control Channel (PDCCH)for a RAR message that will be sent by the Target SeNB 105.

Once the RRC Connection is reconfigured, the UE device 106 transmits anRRC Connection Reconfiguration Complete message to the Master basestation 102 via signal 310. Upon receipt of the RRC ConnectionReconfiguration Complete message, the Master base station 102 transmitsan SeNB Reconfiguration Complete message to Target SeNB 105 to informTarget SeNB 105 that (1) UE device 106 has been reconfigured to switchits secondary connection from Source SeNB 104 to Target SeNB 105, and(2) Target SeNB 105 should be prepared to receive an uplink transmissionfrom UE device 106. The SeNB Reconfiguration Complete message isrepresented in by signal 312.

Upon receipt of the RRC Connection Reconfiguration message, the UEdevice 106 generates a request that the Target SeNB 105 is to transmit aMAC message to the UE device 106, as discussed above. The UE device 106transmits the request to the Target SeNB 105 in an uplink transmission124. The transmission of the request to the Target SeNB 105 isrepresented by signal 314.

Upon receipt of the request, the Target SeNB 105 generates the specificMAC message indicated in the request from the UE device 106. The TargetSeNB 105 transmits the requested MAC message (e.g., a UE ContentionResolution Identity MAC Control Element or a RAR) to the UE device 106.The transmission of the MAC message is represented by signal 316. Insome examples, the MAC message also contains the TA information neededfor the UE device 106 to synchronize its uplink transmissions to theTarget SeNB after the SeNB Change procedure is complete.

FIG. 4 is a flowchart of an example of a method in which a UE devicerequests that a Target SeNB transmits a MAC message to the UE device.The steps of method 400 may be performed in a different order thandescribed herein and shown in the example of FIG. 4 . Furthermore, insome examples, one or more of the steps may be omitted. Moreover, inother examples, one or more additional steps may be added.

The method 400 begins at step 402 with generating, at UE device 106, arequest that Target SeNB 105 is to transmit, to the UE device 106, aspecific MAC message. At step 404, the UE device 106 transmits therequest to the Target SeNB 105 in an uplink transmission. At step 406, aPhysical Downlink Control Channel (PDCCH) Random Access (RA) Responsewindow is configured, and the UE device 106 monitors the PDCCH for therequested MAC message during the PDCCH RA Response window.

At step 408, the UE device 106 determines a Random Access Radio NetworkTemporary Identifier (RA-RNTI), which is used to confirm that the MACmessage received from the Target SeNB 105 is intended for the UE device106. At step 410, in response to receiving the request, the Target SeNB105 generates the requested MAC message and transmits the requested MACmessage to the UE device 106. At step 412, the UE device 106 determineswhen the SeNB Change procedure (e.g., from Source SeNB 104 to TargetSeNB 105) is completed for the UE device 106, based at least partiallyupon when the UE device 106 receives the requested MAC message.

Clearly, other embodiments and modifications of this invention willoccur readily to those of ordinary skill in the art in view of theseteachings. The above description is illustrative and not restrictive.This invention is to be limited only by the following claims, whichinclude all such embodiments and modifications when viewed inconjunction with the above specification and accompanying drawings. Thescope of the invention should, therefore, be determined not withreference to the above description, but instead should be determinedwith reference to the appended claims along with their full scope ofequivalents.

The invention claimed is:
 1. A method comprising: transmitting, at auser equipment (UE) device, an uplink transmission to a Target Secondarybase station while the UE device is connected to a Master base stationand a Source Secondary base station; and receiving, at the UE device, aUE Contention Resolution Identity Media Access Control (MAC) controlelement from the Target Secondary base station in response totransmitting the uplink transmission; wherein a Secondary base stationChange procedure is completed for the UE device when the UE devicereceives the UE Contention Resolution Identity MAC control element, theSecondary base station Change procedure not including transmission ofRandom Access Channel (RACH) from the UE device to the Target Secondarybase station, the Secondary base station Change procedure not includingtransmission of a preamble from the UE device to the Target Secondarybase station.
 2. The method of claim 1, further comprising: receiving,at the Target Secondary base station, a Secondary Base StationReconfiguration Complete message from the Master base station, whereinthe uplink transmission is transmitted after the Secondary Base StationReconfiguration Complete message is received at the Target Secondarybase station.
 3. The method of claim 1, further comprising: receiving,at the UE device, a Radio Resource Control (RRC) ConnectionReconfiguration message from the Master base station, the RRC ConnectionReconfiguration message including uplink grant information, wherein theuplink transmission is transmitted based on the uplink grantinformation.
 4. A user equipment (UE) device comprising: a transmitterconfigured to transmit an uplink transmission to a Target Secondary basestation while the UE device is connected to a Master base station and aSource Secondary base station; and a receiver configured to receive a UEcontention Resolution Identity Media Access Control (MAC) controlelement from the Target Secondary base station in response totransmitting the uplink transmission, wherein a Secondary base stationChange procedure is completed for the UE device when the receiverreceives the UE Contention Resolution Identity MAC control element, theSecondary base station Change procedure not including transmission ofRandom Access Channel (RACH) from the transmitter to the TargetSecondary base station, the Secondary base station Change procedure notincluding transmission of a preamble from the transmitter to the TargetSecondary base station.
 5. A processer for a user equipment (UE) devicecomprising: a memory configured to store at least a program, wherein theat least a program comprises: a first process to make the UE devicetransmit an uplink transmission to a Target Secondary base station whilethe UE device is connected to a Master base station and a SourceSecondary base station; and a second process to make the UE devicereceive a UE Contention Resolution Identity Media Access Control (MAC)control element from the Target Secondary base station in response totransmitting the uplink transmission, wherein a Secondary base stationChange procedure is completed for the UE device when the UE devicereceives the UE Contention Resolution Identity MAC control element, theSecondary base station Change procedure not including transmission ofRandom Access Channel (RACH) from the UE device to the Target Secondarybase station, the Secondary base station Change procedure not includingtransmission of a preamble from the UE device to the Target Secondarybase station.
 6. A Target Secondary base station comprising: a receiverconfigured to receive an uplink transmission from a user equipment (UE)device connected to a Master base station and a Source Secondary basestation; and a transmitter configured to transmit a UE ContentionResolution Identity Media Access Control (MAC) control element to the UEdevice in response to receiving the uplink transmission, wherein aSecondary base station Change procedure is completed for the UE devicewhen the UE device receives the UE Contention Resolution Identity MACcontrol element, the Secondary base station Change procedure notincluding reception of Random Access Channel (RACH) by the receiver fromthe UE device, the Secondary base station Change procedure not includingreception of a preamble by the receiver from the UE device.